I spoke with Chris Hillabrant, regional VP of engineering and operations for T-Mobile, about the company’s network expansion and how the faster available speeds are changing the way consumers use mobile broadband. “In New York, where HSPA+ is available, we’ve seen a 700 percent increase in demand for data,” Hillabrant told me. “And in Philadelphia, we saw nearly 40 percent growth in traffic in the first 40 days of availability.” So how long can T-Mobile’s HSPA+ network handle the growing demand?

“We feel very good about our growth,” Hillabrant said when asked that very question. “Our fiber [backhaul] facilities are highly scalable and we have plenty of wireless spectrum in the big markets, plus efficiencies are gained as we get faster devices on the network. I don’t see any reason we can’t continue to ride the wave ahead of data demand.” Indeed, Hillabrant sounded calm and confident about both backhaul and wireless supply — a refreshing position considering larger U.S. carriers like AT&T are moving from unlimited smartphone data plans to tiered pricing to help manage the supply of data services.

With Verizon and AT&T still using standard 3G technologies, T-Mobile’s HSPA+ network is a closer comparison to Sprint’s 4G offering, which uses WiMAX. Indeed, T-Mobile claims “4G speeds” now when discussing the maturing infrastructure — a clear swipe at Sprint. Semantics and verbal positioning aside, T-Mobile’s new network actually compare favorably to that of Sprint’s, both in speeds and coverage.

After my conversation with Hillabrant, it occurred to me that the iPhone-AT&T phenomenon may have been the best thing to happen to T-Mobile in some time. With all of the focus on iPhone owners using up a disproportionate amount of AT&T’s network — AT&T data demand is up more than 5,000 percent since the introduction of the iPhone, as discussed in a recent GigaOM Pro report (subscription required) — the spotlight has been off of T-Mobile. And that has given the No. 4 carrier in the U.S. some quiet time to ramp up a faster wireless network that covers more customers while nobody was looking. By the end of this year, when completion of the HSPA+ rollout is expected, T-Mobile figures it will be able to cover 185 million POPs with 21 Mbps wireless access and plenty of fiber backhaul to keep the data flowing.